Process of making pigments from lead ores



May 7, 1935. 4 N. c. cHRlsTENsEN 2,000,661

PROCESS OF MAKING PIGMENTS FROM LEAD ORES May 7, 1935. N. c. cHRlsTENsEN I PROCESS OF MAKING PIGMENTS FROM LEAD ORES Filed Oct. l2, 1931 3 Sheets-Sheet 2 www Mwmw m e m k R3 mm m6 l@ s w May 7, 1935- 0 N. c. cHRlsTENsEN 2,000,661

PROCESS OF MAKING PIGMENTS FROM LEAD ORES Filed Oct. 12, 1931 3 Sheets-Sheet 3 n Il 1| n n ll u' INVENTOR 7Zz'eZ5 G/zrLSZezsen/ Patented May 7, 1935 PATENT OFFICE i PROCESS F MAKING PIGMENTS FROM LEAD ORES Niels C. Christensen, Salt Lake City, Utah Application october 12, 1931, Aserial No. 568,512

Claims.

This invention relates to the manufacture of white lead pigments, such as the normal or basic carbonates, chlorides, and sulphates, etc., from lead ores and crude lead products. It is espe- Y 5 cially applicable to the direct manufacture of these lead salts from lead sulphide ores in connection with the brine leaching processes described in my U. S. Patents No. 1,539,711, and others, and from brine leaching processes for the "covery of lead from oxidized ores and from lead products such as lead sulphate. The process avoids the necessity of smelting these ores and products for the recovery of the lead andthe necessity of rening the lead bullion before converting the leadA into the final products. The process makes these products directly from-the ore with a minimum expenditure of time and Vlabor and produces pigments of thev highest quality as to tinting strength and hidingpower.l Slightly different methods of carrying out the process are described in this application and in the copending applications No. 568,511 and No. 568,513. Y The accompanying drawings illustrate the application of the process to the treatment of lead ores and other lead products, and to the treatment of lead chloride or lead sulphateproduced by methods other than those described herein. Figure 1 shows a general flow sheet of the process as applied tothe treatment of lead ores and lead products. Fig. 2, consisting of six curves, shows the percentage of the total lead, held in solution as PbClz in NaCl brines of varying concentrations, Which is precipitated from the hot (substantially boiling) solution by treatment of the solution with different molecular4 equivalents of .Ca(OH)2 to the PbClz (the suspension of Ca(OH) 2 being stirred into the hot brine and the Ymixture agitated for 1Q minutes). Curve A is for equimolecular proportion of Ca(OH)2 to PbClz i. e., 1:1 and curves B, C, D, E and F respectively 74 1%, 1/2, and molecular proportions of Ca(OH)2 to one molecular proportion of PbClz in solution. Fig. V8 consisting of eight curves shows the percentage ofthe total lead held in solution in NaCl brines of different concentrations which is precipitated from the hot (substantially boiling) brine by the addition of different molecular proportions of Ca(OH)2 to PbClz. Curves G, H, I, H, K, L, M, and N are respectively for 1% (water), 4.76%, 9.%, 13.0%, 16.7%, 20.%, 23.1%, and 25.9% NaCl brines respectively. Y

The general method of carrying out the process for the treatment of lead sulphide ores (or oxidized ore or other lead product as later described), as illustrated in Fig. 1 is briefly as follows: the finely ground lead ore or concentrate (or other lead product) is agitated with a hot concentrated NaCl brine (with Y. hydrochloric acid, if necessary) in the leaching agitatorL (I). If lead sulphide ore is being treated a slight excess of HC1 above, the amount theoretically required, is necessary to dissolve the lead, and the silver in the galena as indicated in the following equation: PbS-1-2HCl=PbCl2-}H2S. To secure a substantially complete extraction of the lead from sulphide ores or concentrates requires from to 45 minutes treatment with an excessy of from one half to one percent free H Cl in the brine at the end of the treatment. With oxidized ores practically no excess acid is required. vThe hot pregnant solution is separated from the residue of leached ore in the lter (2) the residual pregnant solution being washed out first with a hot brine wash followed by a water wash. 'Ihe tailings from this treatment may be floated to recover the residual sulphides such as pyrite, etc., containing the residual silver and gold. The hot pregnant solution carrying the lead and silver and impurities such as zinc, iron, manganese, etc., goes to the neutralizer (3) where the residual I-IzS (from the treatment of the sulphide ores only) carried in solution is first oxidized by treatment with a small amount of oxidized ore containing soluble ferric oxide (or other suitable oxidizer PbOz) and the acid thereafter neutralizedwith lead carbonate or mixed lead zinc carbonate ore which precipitates ferrie iron from solution. After this neutralization the ferrous iron and the manganese are removed by agitating the solution with a small excess of the oxidized ore and a suitable oxidizing agent, preferably a solid oxidizer such as PbOz so that a slight excess may be used without being carried'into the next step of the process. The small amount'of oxidized ore added in the rst step of this treatment dissolves in the excess of acid forming ferrie chloride which destroys any HzS as indicated below:

Fe2O3-l-6HCl=2FeCls-|3H2O 2FeCl3-l-H2S=2FeCl2-|2HC1+S The excess FeCl3 and residual acid in solution are neutralized in the second step of this treatment as indicated below;

3PbCO3+2FeC13+3H20= SPbClz-l-ZFe (OH) a-i-BCOZ PbCO3-l-2HC1=PbCl2-l-H2O|C0g The ferrous iron and manganese in the solution are oxidized and precipitated out of solution in the third step of this treatment as indicated by the following chemical equations by means of lead peroxide and oxidized ore:

Zinc carbonate ore may be used for this neutralizing step and the zinc may be recovered as a sulphide or hydroxide as later described. This treatment with oxidized ore and oxidizing agent also removes arsenic and other impurities from solution. The residue of oxidized ore and the precipitated impurities are separated from the purified solution in the iilter (d). The pure neutral pregnant solution thus secured, carrying silver, lead, and Zinc, and perf haps copper and cadmium, in solution now passes through the silver precipitator (5) in which the silver (and copper) is precipitated and removed by treatment with metallic lead, preferably lead` The precipitated silver is separated lution in the filter (6) p The lead present in the hot pregnant lead brine from the silver precipitation is now precipitated by one of the two following methods as indicated by the two methodsA and B shown on the flow sheet in Fig. l. In method indicated as A in Fig. 1 the lead is precipitated by adding Ca(OH)2 to the hot pregnant brine in the amount required to substantially completely precipitate the lead as a hydroxide. As will be noted by reference to Figs. 2 and 3 itis not possible to completely precipitate the lead from a hot concentrated rNaCl brine as an oxych'loride or a hydroxychloride. VAs shown in curves D, E and F, the hydroxychloride (or hydrated oxychloride) is only formed to any` appreciable extent in dilute or relatively dilute brines carrying less than 15% NaCl, and that as shown in curves A, B, C, and G, H, I and J, to secure a practically complete precipitation of the lead from concentrated or relatively concentrated brines it is necessary to use more than W4 of an equimolecular proportion of Ca(OH)2 to PbClz in solution, indicating that there is only a relatively small amount of the hydroxychloride formedin concentrated brines containing more than 17 1/% to 2()%'NaCl. As shown in curves D, E and F (and G, H, I) the oxychloride is formed completely and with ease'only in solutions containing between 5% and 10% NaCl. As Yshown in curves B and C, and L, M and N some hydroxy chloride may, however, be found in the concentrated and relatively concentrated brines, since substantially all the lead is precipitated from 'brines containing over 10% NaCl by seven-eighths'of the chemical equivalent of Ca(OH)2, and in brines containing over 15% NaCl by three-quarters of the chemical equivalent of Ca(OH)2'. In the making of the pigments described by tlie method described in the following, the lead is preferably precipitated from the chloride brines by the use of Ca(OH) 2 in amount approximately equal to seven-eighths, or slightly less, of the chemical equivalent of Ca(OH)2 to the lead in solution. As 10W as three-quarters of the chemical equivalent may be used but the proportion stated above is kpreferred in the making of basic carbonate and basic sulphate, though the larger proportion (seven-eighths) may be used in making the basic chloride (hydroxychloride) The hydroxychloride formed by this process of precipitation remains in the finished product as such and is probably the cause of the superior properties of the basic sulphate and basic carbonate pigments made by this process. The precipitate thus secured lfrom the hot concentrated brines by complete precipitation with Ca(OH)`z in the precipitator (i) is therefore largely lead hydroxide carrying some oxychloride, unused Ca(O1-I)2 and occluded chlorides. This product is filtered out of the barren lead brine in the filter (8) and treated with suitable acids in from the so- Water solution to make basic lead salts of the desired composition as more fully described below. Acids, the basic lead salts of Which are insoluble, are preferably used in this step.

The solution from the lter (8) carries in solution only Zinc and perhaps cadmium and perhaps a trace of lead. These metals (except zinc) are precipitated by means of metallic zinc (preferably zino dust) in the precipitator (9) and filtered out of the solution in the iilter (l0). The hot brine now contains only zinc in solution which is removed by precipitation with lime, or as a zinc sulphide by precipitation with B2S and a suitable lime compound in the precipitator (Il) as indicated in the following equations and as described in my U. S. Patents 1,793,906 and 1,886,162

The precipitated Zn(OH)2 or ZnS is filtered out of the solution in the filter i2) and the barren brine is passed through the concentrator (I3) together with the Wash solutions from the diercnt ltering and washing operations, the mixed solution being thus heated and concentrated for use again in the leaching of more cre. The solution at this point contains CaCl2 equivalent to the acid consumed in dissolving the soluble material in the ore. The acid used in the process is preferably H2504. It may be added to the ore and the brine at the entrance to the agitator (l). The H2804 thus added reacts with the CaCl2 to form HC1 in solution and precipitate CaSO4 which is discharged with the leached residue. If desired the H2804 may be added to the concentrated brine in the precipitator (M) before its entrance to the agitator (I) and the precipitated CaSO4 may be recovered from the solution in the iilter (l5) for use in making gypsum plaster or for other purposes. The hot concentrated acid brine thus formed is used over again 'in the leaching operation as previously described.

The conversion of the precipitated lead hydroxide product (from the filter B) to the desired normal or basic lead salts is carried out by the addition of the required amount of the desired acid to the emulsion of the hydroxide in Water and by grinding in the presence oi Water until the desired stable salt is formed. In this Way any of the insoluble normal or basic or hydroxy salts of lead may be formed such as the lead hydroxychlorides, and the normal and basic lead sulphates, carbonates, silicates, etc. The manner of carrying out this procedure for some of these products and their characteristics are brieiiy described below.

To convert the lead hydroxide precipitate from the filter (8) to lead hydroxychloride, it is mixed with sufficient HC1 solution in the mixer (l5) and then ground in the pebble mill (Il) to secure a uniform product after which it is treated with Water in the washer or treater (i8) to remove any residual CaCl2 and NaCl and form a stable compound and finally iiltered on the filter (i9). The treater (l 8) is arranged to treat the ground product in counter-current With Water so that the first step of the treatment is the removal of the CaCl2 formed by the first reaction in the grinding operation and the second step is a relatively long time counter-current treatment on water. If desired the CaCl2 formed during the grinding operation may be removed by iiltration before the product passes to the treater. I The product from the `iilter may be dried to form a paste as desired.

. water at the entrance to the cooler.

The PbClz thus precipitated is ltered out of the solution in the hlter (23) and the cooled solution passed through the heating section (22) of the heat interchanger and sufcient Ca(GEl)2 is added in this heating operation to precipitate the lead remaining in solution as a hydroxide as previously described for the method A. The lead hydroxide compound is ltered out of the solution in the lter (iii) and the lead iree brine is then treated for the recovery of the zinc and thereafter mixed with the wash solutions and concentrated ai d heated for reuse in the process as previously described for the method A, any excess of PbClz precipitated inthe cooler (261) may be added to the solution in the heater and precipitator (22) and thus be converted to the hydroxide. The coolinfy and heating (and precipitating) operations may be carried out in separate apparatus instead oi" the counter-current heat interchanger (2 i) as shown, the latter being preferred on account of the saving in heat.

The conversion of the lead chloride and lead hydroxide into the desired basic lead compounds is carried out in the modification claimed in the present case, as follows: A. sufficient proportion of the PbClz from the lter (23) to form the normal constituent ci the basic compound together with. an eduimolecular proportion of a calcium salt of the desired acid, or an equivalent mixture of CMO-EM and the acid, is mixed the lead hydroxide product from the lter (2a) in the mixer (is) and gro-und with water in pebble mill (il) and agitated with water in the treater (i8) and finally ltered on the lter (i9) and dried or made into a paste with oil as previously described. The making of the individual pigments is carried out as follows:

In making lead hydroxychloride the PbClz and the Pb 0ll 2 precipitate are mixed in the proper proportion and ground and treated with water y as described, the hydroxychloride being formed as indicated in the following equation:

During the treatment any residual lime in the precipitated lead hydroxide product left by the formation of a small amount of hydroxychloride during the precipitationwith lime, is converted to the hydroxychloride as indicated below:

2PbCl2-i-Ca(Ol-l) 2=2Pb (OH)Cl+CaCl2 In making the basic lead sulphate an equivalent of CaSOi, preferably made in the process as described and coming from the filter (i5) is mixed with the PbCl2 and the Pb(OI-I)2 precipitate and ground and treated as described to form the basic sulphates as indicated below:

PbClz-l-CaSOi-l-PMOH) 2:

PbSOiPb (OH) 2 -I-CaClz Any residual lime reacts with oxychloride in the lead hydroxide precipitate to form the basic sulphate and CaClz as indicated in the following equation:

2Pb(Ol{) Cl`-|-Ca(O-H) z-l-2PbSO4:

The basic lead carbonate is made by the use of nely ground CaCO3 instead of the CaSOi as shown in the following chemical equations:

Residual lime reacts with the oxychloride in the lead hydroxide precipitate being converted into CaClz as indicated below:

The reaction between the solid calcium salts and the lead chloride, orA lead hydroxychloride, is quite rapid in the rirst stages-of the process, but in the later stages becomes relatively very slow and it therefore requires prolonged treatment with water to complete the reaction and bring about the removal of all the residual calciurn as calcium chloride. The presence oi vCaClz or NaCl in any considerable concentration in the water slows up or inhibits this nal reaction and fresh water is thereforeL necessary or preierred, in order to cut down vthe time of treatment required to removethev residual calcium in the product. This-,final treatment with water to bring the reaction to completion and to remove residual calcium in the pigment isV an essential and important part of the process, since if any considerable amount of calcium salt is left in the pigment, the paint lilm containing the pigment may be damaged'by contact with moisture due to the formation of CaClz in the pigment.

The basic lead salts such as the basic carbonate and basic sulphate formed by the method (B) as described in the foregoing will always contain some hydroxychloride in excess of the amount formed in the precipitation 'of the lead hydroxide, due to the Vformation of this salt in treatment in the dilute brines in the pebble mill (Il) and treater (i8) due to the back reaction which tends to go on in a brine as indicated in the following equations:

uble are removed in the washing operation leaving the insoluble hydroxide behind, the pigments thus formed being thus mixed with a considerin the pebble mill or grinder HB and washed with water in the treater (lSB) to form the normal salt as indicated in the equations below:

The normal salt thus formed is iiltered out in the iilter (i933) and this product .is mixed with the lead hydroxide precipitate from the filter (24) in proper proportion in the mixer (It) and. ground in the pebble mill (Il) and agitated with water in the treater (IS) to form the desired vbasic salts as indicated in the Afollowing equation: f f

The hydroxychloride thus secured is a pure white permanent pigment having a tinting strength and hiding power equal to or better than ZnO. The reactions occurring during this treatment are indicated in the following equations, the principal reaction being as follows: l

Any small residue of Ca(OI-I)2 included in the precipitated lead hydroxide due to absorption of chlorides or to the formation of a small amount of hydroxychloride is converted to CaClz by the HC1 leaving a clean hydroxychloride as indicated in the following equation:

The more basic hydroxychloride, PbCl2-2Pb(OH) 2 may be made as described but is not as permanent a pigment as the Pb(OH)Cl, as it tends to turn brown uponexposure to light.

The making ofvlead sulphate or the basic lead sulphates is carried out'in the same manner as described above except that the required amount of H2804 instead of HC1 is added in the mixer (H3). By varying the ratio of H2SO4 to Pb in the precipitated lead hydroxide product, basic salts or mixtures of any desired composition between the normal sulphate PbSO4 and the more basic sulphate PbSO4-2Pb(OI-I)2 may be secured. The normal sulphate formed by this neutralization of the lead hydroxide and grinding and treating v'with water gives a permanent white pigment having Substantially the same tinting strength and hiding power as the sublimed white lead or socalled basic sulphate now in common use. The basic sulphate PbSO4-Pb(OI-I)2 is a permanent white pigment having a tinting strength and hiding power considerably superior to thebasic white leads now on the market. The more basic sulphate PbSOi2Pb OH 2 has a much higher tinting strength and hiding power than the less basic salt but is not as permanent a pigment as it shows a tendency to turn yellow upon exposure to light, The reactions occurring in the manufacture of these sulphate pigments are indicated as follows:

Any oxychloride and residual lime in the lead hydroxide precipitate are converted to the sul- 'phate or basic sulphate as indicated in the following equations:

and the CaClz is washed out in the grinding and treatment with water. l

The formation of the leadY carbonates and basic lead carbonates is carried out by treating the required proportion of the lead hydroxide precipitate with CO2 in a suitable pulp spray (24) of the type shown in my U. S. Patent 1,452,863 or tumbling barrel (25) and then mixing this carbonated product with the remaining lead hydrox- Vide precipitate in the mixer (i6) and grinding the mixture in the pebble mill (IT) and treating with Water in the treater (i8) Yand thereafter filtering and drying as described. By this method, by varying the proportion of the lead hydroxide precipitate which is carbonated, white lead pigments varying from Vthe normal carbonate tothe ordinary basic carbonate 2PbCO3Pb(OH)2, (or more basic mixtures) may be secured. The normal carbonate thus prepared has substantially the same tinting` strength and hiding power as the basic white leads now on the market, while the basic white lead thus prepared has a much higher tinting strength and covering power than the ordinary white leads now in common use. The salts which are more basic than the basic carbonate 2PbCO3Pb(OH)z, are not as permanent as the less basic, having a tendency to turn yellow upon exposure to light, The reactions taking place in the treatment are indicated in the following chemical equations:

Any oxychloride and excess lime in the precipitated lead hydroxide are converted to the carbonate or basic carbonate as indicated below:

In the preparation of any of the above described pigments for commercial use, the wet products from the filter (i9) may either be dried toy secure the dry pigment or may be mixed with the desired amount of oil to form a paste as is a common practice with white lead. The lead hydroxide precipitate used in making the basic lead salts by the method A should be washed free from chlorides as rapidly as possible, before treatment with the diiferent acids to form the basic compounds, since in dilute brines (7l/2 to 12% NaCl and CaClz) there is a back reaction tending to form Pb OH Cl as indicated in the following equations:

This would result in the formation of hydroxychloride somewhat in excess of the amount formed in the precipitation and would slightly increase the amount of hydroxychloride in the nal product. Though' the small propoltion of hydroxychloride in the final products made by this process gives the basic carbonate and basic sulphate their superior properties, the preferred method of treatment consists in securing this hydro-xychloride by the use of less than the chemical equivalent of Ca(OI-I) z in the precipitation rather than by treatment of the precipitation to cause a reversion to the hydroxychloride during subsequent washing treatment as described above.

The CaSO4 and Ca(OH)2 being slightly soluble are removed in washing leaving the hydroxychloride. The tendency to thus form oxychlorides is much stronger in the case of the basic sulphate than the basic carbonate. n

The making of the lead pigments mentioned in the foregoing may also be carried out as indicated in method B of the flow sheet of Figure l. En this method the clean brine from the silver precipitator is passed through the cooling section (2G) of the counter-current heat interchanger (2i) and cooled to precipitate PbClz from the solution. If necessary to secure suicient PbClz the solution may also be diluted with By removing the CaClz formed in the precipitation of the Pb(OH)2 and normal salts before mixing these and grinding and treating with Water to form the basic salts, the amount of hydroxychloride is reduced to a minimum and substantially pure products formed, but this is not the method preferred in this process.

The foregoing description relates primarily to the treatment of sulphide ores of lead but it will be apparent that it is also applicable to the treatment of oxidized or carbonate ores in substantially the same manner, i. e., these ores may be leached with hot acid brine in the leaching agitator (l) and the solution thereafter puried as described and the lead may be recovered from the solution in the manner described and illustrated in the flow sheet of Fig. l, and may be converted to the desired pigments by either of the methods A or B as described in the foregoing. Lead sulphate or lead chloride from other sources may also be treated in a similar manner by dissolving in the hot brine, Which after purification may be treated as described, for the recovery of the lead and manufacture of the desired lead products as described. n the case of the lead sulphate the CaClz, made in the solution as described by treatment of the PbClz with the Ca(OH)2 and other lime salts to form the desired products as described, reacts with the lead sulphate in the concentrated brine to form PbClz in solution and to precipitate 02.504 which may be removed by filtration in the iilter (2) 'following the dissolving of the PbSO4 in the leaching agitator or dissolver (i).

Having described my invention what I claim and desire to patent is:

1. The process of making basic lead pigments from lead ore material in which the lead is recovered from said ores and the like in a chloride brine, Which consists in precipitating a portion of the lead from said brine as lead chloride and precipitating another portion of the lead from said brine by adding thereto an amount or" calcium hydroxide which is substantially less than chemically equivalent to the lead in said brine, but more than three-quarters of said equivalent, to produce a precipitation of lead hydroxide containing some lead hydroxychloride, and mixing said precipitates in the proper proportion with a calcium salt of an lacid or which the normal and basic lead salts are insoluble in amount substantially chemically equivalent to the lead chloride in said mixture, and treating said mixture with water and washing out the CaClz formed during said treatment and treating the residual product With more Water to remove residual calcium as CaClz and form a stable basic lead pigment containing the acid radical of the above said calcium salt.

2. The process of making basic lead pigments from lead ore material in which lead is recovered from said ores and the like in a chloride brine, which consists in precipitating a portion of the lead from said brine as lead chloride and precipitating another portion of the lead from said brine by adding thereto an amount of calcium hydroxide which is substantially less than chemically equivalent to the lead in said brine, but more than three-quarters of said equivalent,

to produce a precipitation of lead hydroxide containing some lead hydroxychloride, and mixing said precipitates in the proper proportion With a calcium salt of an acid of which the normal and basic lead salts are insoluble in amount substantially chemically ,equivalent to the lead chloride in said mixture and grinding said mixture in Water andwashing out the CaClz formed during said treatment and treating the residual product with more Water to remove residual calcium as CaClz and form a stable basic lead pigment containing the acid radical of said calcium salt.

3. The process of making basic lead carbonate from lead ore material in which lead is recovered from said ores and the like in a chloride brine, which consists in precipitating part of the lead from said brine as lead chloride and precipitating another portion of the lead from said brine by adding thereto an amount of calcium hydroxide which is substantially less than chemically equivalent to the lead in said brine, but more than three-quarters of said equivalent, to produce a precipitation of lead hydroxide containing some lead hydroxychloride, and mixing said precipitates in the proper proportion With a proportion of i'inely divided calcium carbonate chemically equivalent to the lead chloride in said mixture and treating said mixture with Water and washing out the CaCl2 formed during said treatment and treating the residual product with more Water to remove residual calcium as CaClz and form a stable basic lead carbonate pigment.

4. The process of making basic lead sulphate from lead ore material in which lead is recovered from said ores and the like in a chloride brine, which consists in precipitating a portion of the lead from said brine as lead chloride and precipitating another portion of the lead from said brine by adding thereto an amount of calcium hydroxide which is substantially less than chemically equivalent to the lead in said brine, but more than three-quarters of said equivalent, to produce a precipitation of lead hydroxide containing some lead hydroxychloride, and mixing said precipitates inproper proportion with a proportion of nely divided calcium sulphate chemically equivalent to the lead chloride in iirst said mixture and treating said mixture with Water, and Washing out the CaClz formed during said treatment and treating the residual product With more Water to remove residual calcium as CaClz and form a stable basic lead sulphate pigment.

5. The process of making lead precipitate containing hydroxychloride from lead ore material in which lead is recovered from said ores and the like in a chloride brine, Which consists in precipitating part of the lead from said brine as lead chloride and precipitating another portion of the lead from said brine by adding thereto an amount of calcium hydroxide which is substantially less than chemically equivalent to the lead in said brine, but more than three-quarters of said equivalent, to produce a precipitation of lead hydroxide containing some lead hydroxychloride, and mixing said precipitates in the proper proportion and treating said mixture with Water to remove residual calcium as CaClz and form a `stable pigment which contains lead hydroxychloride.

NIELS C. CHRISTENSEN.

Certificate of Correction Patent No. 2,000,661. l May 7, 1935. NIELS C. CHRISTEN SEN It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 1, first column, line 44, for 8 read 3; page 2, second column, line 48, for emulsion read suspension; and page 3, rst column, line 46, strike out the formula and insert insteadand that the said Letters Patent should be read with these correctionsv therein that the same may conform to the record of the oase in the Patent Ooe.

Signed and sealed this 18th day of June, A. D. 1935.

[SEAL] LESLIE FRAAZER, Acting Commissioner of Patents. 

